NetScreen 5XP firewall

We recently purchased new Netscreen 5XP firewall. I want to configure this firewall as below structure.
We have Cisco Router (2600 Series)IP address is 64.x.x.1. Router to a NetGear switch is connected. Netgear switch to servers (IP address 64.x.x.2 to 64.x.x.20). one of the server IP address 64.x.x.2 It is proxy server. Proxy server to 3com HUB. Hub to other servers and desktop computers.Those servers address ranging from 192.168.x.1 to 192.168.x.200. I want to connect Netscreen 5XP firewall between Cisco Router and a switch (64.x.x.2 to 64.x.x.20). I want to assign a IP address to netscreen firewall is 64.x.x.12. Which mode I should use. Is it better to use NAT or Transfer mode method?. Please tell me how to configure?